The present invention relates to a brake power proportioning device for a motor vehicle, to an elastic element for a brake power proportioning device and to a corresponding vehicle.
For proportioning the brake control force between the master brake cylinders of the front axle and rear axle, a balance beam is normally used in the motor vehicle. The brake control force is therefore proportioned at the inverse ratio of the lever arms of the balancing beam onto the master brake cylinders. In this case, adjusting this ratio as a function of the loading of the motor vehicle is already known. The adjustment is carried out, for example, after the loading of the motor vehicle.
During a braking operation, however, the wheel load proportioning between the front and rear axle is dynamic, whereby the ideal brake power proportioning describes a parabola, whereas the brake load proportioning adjusted by a balance beam represents a straight line. The brake power proportioning is therefore normally adjusted for a value close to the maximally obtainable deceleration during a braking operation. For this reason, at the start of the braking operation and until the maximal deceleration has been reached, one axle, normally the rear axle, does not optimally participate in the deceleration of the motor vehicle. The result is a lengthening of the braking distance.
DE 25 23 061 A1 describes a brake power proportioning device for a motor vehicle where the brake control force is proportioned by a balance-beam-like device at a variable ratio onto the master brake cylinders of the front and rear axle of the motor vehicle. The balance-beam-type device is configured so that a lever arm adjustment, which adjustment is continuously a function of the brake control force, can be achieved for a constant course of the braking power proportioning onto the master brake cylinders. For this purpose, the balancing-beam-type device is provided as an unstably disposed, dimensionally stable triangle of forces. When a braking operation is initiated, existing elasticities and/or idle paths of the braking system result in an unequal proportioning of the brake control force onto the two master brake cylinders. When the brake control force is increased, the unstable bearing will then result in an increasing inequality of the proportioning of the brake control force. For implementing this solution, however, complicated restricted guiding devices are required in the case of the braking system as well as braking systems that are not ideal or have a special construction for providing a respective elasticity or idle path. Also, such restricted guiding devices generate additional friction and require additional space in the motor vehicle.
DE 11 19 136 describes a brake power proportioning device with a spring elastic. When a certain brake control force is exceeded, a discontinuous change, that is, a jump, is achieved by a high-expenditure lever system when the braking power is proportioned onto the two master brake cylinders.
An object of the present invention is to provide a motor vehicle brake power proportioning device that provides a continuous lever arm adjustment as a function of the brake control force, has a simple construction and can be used for arbitrary pressure-type braking systems.
According to the invention, it is provided that, for achieving the lever arm adjustment as a function of the brake control force, at least one section of the balance-beam-type device is constructed to be continuously deformable as a function of the brake control force. As a result of the use of the element according to the invention, which can be deformed as a function of the brake control force, a lever arm adjustment of the balance-beam-type device, which is continuously a function of the brake control force, for arbitrary pressure-type braking systems in the motor vehicle can take place.
In other words, the present invention utilizes no strengthening of already existing instabilities or elasticities of an existing braking system but provides the latter itself by way of an element that can be deformed as a function of the brake control force. In particular, the braking system can have an ideally stiff construction with respect to the brake pedal travel i.e., the idle path and the volume incorporation. A special construction of the braking system is also not required. Particularly, no restrictions exist with respect to used diameters of hydraulic cylinders or other components. A particularly simple and cost-effective implementation is achieved because of the elimination of additional restricted guiding devices with their friction and space requirement.
A particularly preferred embodiment of the invention provides that the balance-beam-type device is constructed as a triangle of forces (also referred to hereinafter as a force triangle), at least one leg of the triangle of forces comprising an element of a defined elasticity. Such elements of a defined elasticity are, for example, springs, gas or elastomers. These elements are selected so that they have an elasticity which is defined under the normal operating loads of the braking system and is significant. Because of the resulting longitudinal change of the at least one leg of the triangle of forces, the ratio of the lever arms and thereby the brake load or power proportioning onto the main brake cylinders is changed. The selection of the geometry of the triangle of forces—that is, the leg lengths and angles, and the stiffness of the element of a defined elasticity (elastic element) achieves an individual adjustment of the brake power proportioning by way of the brake control force. An approximation to an ideal brake load or power proportioning can thereby be represented.
The present invention now achieves for the first time a control of arbitrary braking systems that continuously is a function of the brake control force. A strengthening of material-caused elasticities of components, such as tubes, is therefore no longer necessary. The reason is that the design of a braking system is aimed at minimizing as much as possible specifically these material-caused elasticities. Elasticity in pressure-transmitting components means additional volume incorporation, while elasticity in power-transmitting components indicates an additional path to be covered. Both of these effects lead, however, to a more indirect feeling at the brake pedal with a less precise pressure point, and that is undesirable during a brake application.
With the present invention, a particularly simple construction of a brake load or power proportioning is obtained for a constant brake control force proportioning distribution to the wheel brake cylinders. By the selection of a suitable elastic material, for example, progressive, decreasing or a combination thereof, brake load distributions can be implemented with an arbitrarily definable course. In particular, an adaptation can also take place to a braking system in which the elastic element is under tension for controlling pulled wheel brake cylinders, or in which the elastic element is subject to compression, for controlling pressed wheel brake cylinders.
In an advantageous further development of the invention, a damping member is additionally assigned to the elastic element for the time-delayed application of the brake control force. The background is that, at the moment of the starting braking operation, the ideal brake power proportioning corresponds to the static ratio of the axle loads of a stationary motor vehicle. This is based on the circumstance that a direct proportionality exists between the brake pressure and the static acceleration (change of speed) of the motor vehicle. However, as a result of the acceleration of the vehicle, a dynamic wheel load distribution takes place. At the start of the acceleration operation, the motor vehicle is therefore in a non-static condition, whereby the applied brake pressure “precedes” the actual acceleration. For the time period of a time variation, the defined brake load (power) proportioning therefore does not correspond to the actual acceleration forces transmitted by the axles. Particularly at the start of the braking operation, the rear axle of the motor vehicle could make a higher contribution to the overall deceleration of the vehicle than is triggered by the present system. This can be taken into account by a delay of the adjustment of the brake power proportioning; i.e., by the use of a damping member parallel to the elastic element. This damping member can be adapted individually to vehicle dynamics. In other words, in addition to the brake load proportioning which is a function of the power, a component is used which is dependent on the control speed.
Preferably, the elastic element and/or the damping member are provided to be exchangeable. This permits an individual adaptation to a respectively predefined configuration of the motor vehicle. An exchange is particularly easy if the elastic element is constructed in one piece together with the damping member.